1. Field of the Invention
The present invention relates to a fuel cell separator containing a mixture of conductive material and resin as its main components and a method for manufacturing the fuel cell separator, and particularly relates to a technique for reducing the thickness of the fuel cell separator.
Further, the present invention relates to a fuel cell separator containing conductive material and epoxy resin, and particularly relates to a fuel cell separator made to have high strength.
2. Description of the Related Art
For example, as shown in the schematic perspective view in FIG. 1, a fuel cell separator 10 is formed by erectly providing a plurality of partitions 12 at predetermined intervals on the opposite sides of a flat plate portion 11. To form a fuel cell, a large number of such fuel cell separators 10 are laminated in the direction in which the partitions 12 project (in the up/down direction in the drawing). Then, by this lamination, reactive gas (hydrogen or oxygen) is designed to be circulated in each channel 13 formed by a pair of adjacent partitions 12.
It is required to make a fuel cell compact as a whole for wide use of the fuel cell. To this end, reduction in the thickness of the flat plate portion 11 or the partitions 12 of the fuel cell separator 10 is required. However, the fuel cell separator 10 is generally manufactured by compression molding of a kneaded compound having graphite material and resin as its main components into an illustrated shape. Thus, along with reduction in thickness, compression failure is easily produced at the time of the compression molding. In the present situation, there is therefore a limit to the thickness to be reduced.
Further, since the reactive gas is generally circulated in these channels 13 at a pressure of 0.1-0.3 MPa, strength high enough to prevent the fuel cell separators 10 from being deformed by this gas pressure is required of the fuel cell separators 10. To this end, strength is conventionally secured by blending polyimide resin or the like. Alternatively, fibrous material is blended to enhance the strength. For example, JP-A-63-294610 and JP-A-2000-133281 disclose fuel cell separators in which carbon fibers are blended, and JP-A-4-214072 and JP-A-2000-82476 disclose fuel cell separators in which various fibrous materials are blended.
Nowadays, it is said that electric vehicles mounted with fuel cells will be put into practical use in the near future. To bring the electric vehicles into wide use, it is essential to reduce the price of fuel cells. Several hundreds of fuel cell separators are required in each fuel cell vehicle. Reduction in the cost of such fuel cell separators is important for reduction in the price of a fuel cell. In the above-mentioned method in which polyimide resin is blended, however, the polyimide resin expensive in price becomes an obstacle to reduction in cost.
On the other hand, in each of the methods in which fibrous material is blended, there is a problem that when the fibrous material is blended, the fluidity of a raw material kneaded compound becomes so low that the formability deteriorates. Generally, each fuel cell separator is required to be formed into a finer and complicated irregular shape for the purpose or making reactive gas flow uniformly and at an appropriate flow rate, further facilitating the discharge of the generated moisture, and so on. However, when the fluidity of the raw material kneaded compound is poor, the raw material kneaded compound cannot reach every corner of a mold uniformly at the time of molding, so that the fuel cell separator obtained becomes uneven in the quality of the material. As a result, there arises such a problem that the reproducibility of the fine irregular shape deteriorates. Reduction not only in cost but also in size is demanded in a fuel cell. To this end, respective portions of fuel cell separators have to be thinned. However, when the formability of the raw material kneaded compound is poor, such reduction in the thickness cannot be achieved. Thus, each of the above-mentioned methods in which fibrous material is blended is undesirable to obtain a high-performance and thin fuel cell separator.